1. Field of the Invention
The present invention pertains to a method and apparatus for determining wheel runout and axial stability of the wheels of a motor vehicle. More specifically, the present invention pertains to a method and apparatus for measuring axial stability of vehicle wheel systems and for determining whether or not the wheel suspension and associated mechanisms of a vehicle fall within predetermined tolerances such that alignment is feasible without prior repair or replacement of parts.
2. Terms and Definitions
"Camber" is the angle representing the inward or outward tilt from true vertical of a wheel. Camber is positive if the top of the wheel tilts outward.
"Geometric center line" is the line that runs from a point on the rear axle midway between the rear wheels to a point on the front axle midway between the front wheels.
"Toe" is the angle formed by a front to back line through the wheel compared to the geometric center line. Traditionally, Camber and Toe measurements for a wheel are relative measurements i.e. relative to a vertical plane or to another wheel.
"Roll" is the angle measured about a true axis of the wheel.
3. Description of the Prior Art
Proper maintenance of a motor vehicle typically includes a periodic wheel alignment diagnostic test in order that proper tire wear and safe handling may be achieved. However, many vehicles that are brought into a shop for alignment inspection actually have more serious suspension problems that cannot be corrected by simple realignment. If any of the wheels of the vehicle are seriously out of alignment, excessive or uneven wear of the tires can result and adversely affect the handling and stability of the vehicle. In addition to simple misalignment, a vehicle may have some degree of runout or wobble which indicates that the plane of the wheel is not precisely perpendicular to its axis of rotation. Such problems may be caused by defective bearings, a defective or damaged suspension system, or a defective, worn, or damaged steering system. Numerous devices and systems for determining the alignment of motor vehicle wheels are well known and used throughout the world to facilitate the alignment of wheels supported by a myriad of types of suspension systems.
However, if a vehicle wheel exhibits excessive runout, suspension play, or wheel play, the use of instruments mounted on the wheels may not produce an accurate alignment reading unless compensation is provided. Methods for determining compensation for runout of a wheel of a vehicle are well known and typically include interval measurements of position and orientation of a wheel as it is moved through a series of predetermined positions displaced from a known starting position. The measurement values are then processed to determine angular relations which yield runout characteristics that can be factored into the alignment operations. It is possible to determine and compensate for some wheel play when aligning a vehicle wheel. But, if the wheel suffers from excessive wheel play, then realignment of the wheels is useless.